| With the acceleration of urbanization,the urban area expanded and the area of cultivated land and forest land decreased.The change of underlying surface was bound to have a certain impact on the regional climate.At present,there are many researches on changes in meteorological elements such as temperature,humidity,and precipitation caused by urbanization,but few researches on changes in cloud cover.Cloud is not only an important indicator of climate change,but also an important factor affecting climate change.Therefore,correct response to the impact of urbanization on cloud cover can provide a more comprehensive understanding of urban regional climate and provide a scientific basis for urban ecosystem management.In this paper,the Yangtze River Delta,which has experienced rapid urbanization development,was selected as the research area.Based on the land use data and population density distribution data,the urban and rural stations were divided.Considering the lack of cloud cover data of meteorological stations,the study period was divided into two periods: slow development stage and rapid development stage.Based on the cloud cover observation data of meteorological stations from 1980 to 2003 and MODIS satellite remote sensing data from 2003 to 2018,the UMR(Urban Minus Rural)method was used to analyze the urban-rural differences and variation of annual and seasonal average total cloud cover amount in recent 39 years,and the influence of temperature and water vapor caused by urbanization on the total cloud cover was discussed.The main conclusions of this study are as follow:(1)During 1980-2018,the average annual total cloud cover in the Yangtze River Delta is about 64%.The spatial distribution of total cloud cover in the Yangtze River Delta showed a zonal distribution characteristic with more in the south and less in the north.The high value area is mainly distributed in the southern mountainous area of Zhejiang Province,and the low value area is mainly distributed in the northern area of Jiangsu Province.Summer is the season with the most total cloud cover,about 70%,followed by spring and the least in autumn and winter,less than 60%.(2)In the slow development stage of urbanization(1980-2003),the total cloud cover of urban stations and rural stations in the Yangtze River Delta showed a downward trend,and the downward trend of urban stations was more significant than that of rural stations.The seasonal variation trend was consistent with the annual variation,which indicates that the urbanization led to a downward trend in the total cloud cover in this period.In the rapid development stage of Urbanization(2003-2018),the total cloud cover of urban stations and rural stations in the Yangtze River Delta showed an upward trend,and the increase rate of urban stations was greater than that of rural stations,which was contrary to the variation of the slow development stage,but the difference was not significant.However,the total cloud cover of the urban was lower than that of the rural in both periods.(3)The annual average total cloud cover of most stations in Yangtze River Delta is negatively correlated with air temperature,and positively correlated with vapor pressure and relative humidity.The annual average total cloud cover also has a significant negative correlation with the vapor pressure deficit,the total cloud cover in both urban and rural areas decreased with the increase of VPD in this area.indicating that the factor influencing the variation trend of cloud cover may be the degree of water vapor saturation.(4)Compared with the urban dry island,there is a significant negative correlation between urban heat island and cloud cover difference,that is,the stronger the urban heat island is,the greater the cloud cover difference is,indicating that the urban heat island has a greater impact on the cloud cover difference in the Yangtze River Delta. |
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